1. Field of the Invention
The invention relates to display devices. More specifically, the invention describes a memory resource efficient method, apparatus, and system for using driving LCD panel drive electronics.
2. Overview
Deterioration of image quality for moving images (such as reduced resolution and blurring) referred to as “ghosting” that is due primarily to the slower response time of liquid crystal is a common problem in LCD monitors. Since LCDs rely on the ability of the liquid crystal material to orient itself under the influence of an electric field, the viscous nature of the liquid crystal material causes a response delay that can be longer than the time between successive frames. Ghosting occurs when the luminance value for a frame immediately following any abrupt transitions between luminance levels (i.e., either a falling or a rising transition) deviates significantly from the target luminance value.
A popular technique for reducing or even eliminating these ghosting artifacts, referred to as LC pixel overdrive, is based upon providing an overdrive luminance value (corresponding to an overdrive pixel voltage) calculated to provide the target luminance within the specified frame. Implementation of these LC pixel overdrive techniques typically involves comparing the display data of a new frame to that display data of previous frame or frames. Based upon this comparison, the applied pixel voltage is adjusted such that the target luminance value (or a substantial portion, thereof) is achieved within the specified frame period. Common practice dictates that a frame buffer be used to store the display data of previous frame(s) that is then used to compare to the new frame data. A typical frame buffer can be on the order of a few Megabytes (3-5) in size having access times on the order of a few nanoseconds.
Currently, LCD panels operate in a range of vertical refresh frequency (in the range of approximately 50-60 Hz) that is limited due to many factors (such as the response time of the LC material and the fact that the line period must be of sufficient duration to enable adequate charging and discharging of LCD cells). However, PCs were developed for use with CRT type displays and are designed to generate a display image with a higher vertical refresh rate (such as 75 Hz and 85 Hz) in order to reduce flicker common to CRT technology. However, these higher refresh rates are both unnecessary and difficult to maintain for most LCD panels. Therefore these high refresh rates must be reduced for most LCD panels using any of a number of frame rate conversion (FRC) protocols such that an LCD panel can be used with any video source regardless of its native refresh rate. As with LC pixel overdrive, implementing currently available FRC protocols requires dedicated memory in the form of a frame buffer arranged to selectively store and read out the display data.
As described above, both FRC and overdrive require the LCD display controller have a frame buffer for data manipulation. Enabling both FRC and LC pixel overdrive simultaneously requires higher memory bandwidth than is required for enabling only one of them. Higher memory bandwidth results in higher implementation cost of both the LCD display controller and the frame buffer memory components.
Therefore, being able to selectively enable either FRC or LC pixel overdrive based upon an input vertical refresh rate is very desirable.